Six-Step Commutation of BLDC Motor Using Sensor Feedback

This example uses 120-degree conduction mode to implement the six-step commutation technique to control speed and direction of rotation of a three-phase brushless DC (BLDC) motor. The example uses the switching sequence generated by the Six Step Commutation block to control three-phase stator voltages, and therefore, control the rotor speed and direction. For more details about this block, see Six Step Commutation.

The six-step commutation algorithm requires a Hall sequence or a rotor position feedback value (which is obtained from either a quadrature encoder or a Hall sensor).

The quadrature encoder sensor consists of a disk with two tracks or channels that are coded 90 electrical degrees out of phase. This creates two pulses (A and B) that have a phase difference of 90 degrees and an index pulse (I). The controller uses the phase relationship between the A and B channels and the transition of channel states to determine the speed, position, and direction of rotation of the motor.

A Hall effect sensor varies its output voltage based on the strength of the applied magnetic field. According to the standard configuration, a BLDC motor consists of three Hall sensors located electrically 120 degrees apart. A BLDC with the standard Hall placement (where the sensors are placed electrically 120 degrees apart) can provide six valid combinations of binary states: for example, 001,010,011,100,101, and 110. The sensor provides the angular position of the rotor in degrees in the multiples of 60, which the controller uses to determine the 60-degree sector where the rotor is present.

The controller controls the motor by using the Hall sequence or the rotor position. It energizes the next two phases of the stator winding, so that the rotor always maintains a torque angle (angle between rotor d-axis and stator magnetic field) of 90 degrees with a deviation of 30 degrees.

Note: The Hall sequence can vary. Use the example Hall Sensor Sequence Calibration of BLDC Motor to determine the Hall sequence.

The example supports simulation. You can simulate a plant model containing a three-phase switching inverter along with wye-wound BLDC from Simscape™ Electrical™.

Models

The example includes these models:

You can use these models for both simulation and code generation.

For details of the supported hardware configuration, see Required Hardware in the Generate Code and Deploy Model to Target Hardware section.

Required MathWorks Products

To simulate model:

• Motor Control Blockset™

• Fixed-Point Designer™

• Simscape™ Electrical™

2. For the model mcb_bldc_sixstep_f28379d

• Motor Control Blockset

• Simscape Electrical

To generate code and deploy model:

• Motor Control Blockset

• Embedded Coder®

• C2000™ Microcontroller Blockset

• Fixed-Point Designer

2. For the model mcb_bldc_sixstep_f28379d

• Motor Control Blockset

• Embedded Coder

• C2000 Microcontroller Blockset

• Fixed-Point Designer (only needed for optimized code generation)

Prerequisites

1. Obtain the motor parameters. We provide default motor parameters with the Simulink model that you can replace with values from either the motor datasheet or other sources.

However, if you have the motor control hardware, you can estimate the parameters for the motor that you want to use by using the Motor Control Blockset parameter estimation tool. For instructions, see Estimate PMSM Parameters Using Recommended Hardware.

The parameter estimation tool updates the motorParam variable (in the MATLAB® workspace) with the estimated motor parameters.

2. If you obtain the motor parameters from a motor datasheet or from other sources, update the motor parameters and the inverter parameters in the model initialization script associated with the Simulink models. For instructions, see Estimate Control Gains and Use Utility Functions.

If you use the parameter estimation tool, you can update the inverter parameters, but do not update the motor parameters in the model initialization script. The script automatically extracts the motor parameters from the updated motorParam workspace variable.

Simulate Model

This example supports simulation. Follow these steps to simulate the model.

1. Open the model included with this example.

2. Select either the QEP or the Hall Speed_Feedback radio button in the model.

3. Click Run on the Simulation tab to simulate the model.

4. Click Data Inspector on the Simulation tab to view and analyze the simulation results.

Generate Code and Deploy Model to Target Hardware

This section shows you how to generate code and run the six-step commutation algorithm on the target hardware.

This example uses a host and a target model. The host model is a user interface to the controller hardware board. You can run the host model on the host computer. The prerequisite to use the host model is to deploy the target model to the controller hardware board. The host model uses serial communication to command the target Simulink model and run the motor in a closed-loop control.

Required Hardware

The example supports these hardware configurations. You can also use the target model name to open the model for the corresponding hardware configuration, from the MATLAB® command prompt.

For connections related to these hardware configurations, see LAUNCHXL-F28069M and LAUNCHXL-F28379D Configurations.

Generate Code and Run Model on Target Hardware

1. Simulate the target model and observe the simulation results.

2. Complete the hardware connections.

3. The model computes the ADC (or current) offset values by default. To disable this functionality, update the value 0 to the variable inverter.ADCOffsetCalibEnable in the model initialization script.

Alternatively, you can compute the ADC offset values and update them manually in the model initialization script. For instructions, see Run 3-Phase AC Motors in Open-Loop Control and Calibrate ADC Offset.

4. If you are using a quadrature encoder, compute the quadrature encoder index offset value and update it in the `bldc.PositionOffset` variable available in the model initialization script associated with the target model. For instructions, see Quadrature Encoder Offset Calibration for PMSM.

5. If you are using a Hall sensor, compute the Hall sequence value and update it in the `bldc.hallsequence` variable available in the model initialization script associated with the target model. For instructions, see Hall Sensor Sequence Calibration of BLDC Motor.

6. Open the target model. If you want to change the default hardware configuration settings for the model, see Model Configuration Parameters.

7. Select either the Quadrature Encoder or Hall Speed_Feedback radio button in the target model.

8. Load a sample program to CPU2 of LAUNCHXL-F28379D. For example, you can use the program that operates the CPU2 blue LED by using GPIO31 (c28379D_cpu2_blink.slx), and ensure that CPU2 is not mistakenly configured to use the board peripherals intended for CPU1. For more information about the sample program or model, see the Task 2 - Create, Configure and Run the Model for TI Delfino F28379D LaunchPad (Dual Core) section in Getting Started with Texas Instruments C2000 Microcontroller Blockset (C2000 Microcontroller Blockset).

9. Click Build, Deploy & Start on the Hardware tab to deploy the target model to the hardware and load the variables from the target model to the base workspace.

10. Click the host model hyperlink in the target model to open the associated host model.

For on the serial communication between the host and target models, see Host-Target Communication.

11. In the model initialization script associated with the target model, specify the communication port using the variable target.comport. This variable updates the Port parameter of the Host Serial Setup, Host Serial Receive, and Host Serial Transmit blocks available in the host model.

12. Update the reference speed value in the Reference Speed (RPM) field in the host model.

13. In the host model, select the debug signals that you want to monitor.

14. Click Run on the Simulation tab to run the host model.

15. Change the position of the Motor switch to Start, to start running the motor.

16. Observe the debug signals from the RX subsystem, in the Scope and Display blocks in the host model.